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KEYBOARD(4) FreeBSD Kernel Interfaces Manual KEYBOARD(4)
NAMEkeyboard -- pc keyboard interface
DESCRIPTION
The PC keyboard is used as the console character input device. The key-
board is owned by the current virtual console. To switch between the
virtual consoles use the sequence ALT+Fn, which means hold down ALT and
press one of the function keys. The virtual console with the same number
as the function key is then selected as the current virtual console and
given exclusive use of the keyboard and display.
The console allows entering values that are not physically present on the
keyboard via a special keysequence. To use this facility press and hold
down ALT, then enter a decimal number from 0-255 via the numerical key-
pad, then release ALT. The entered value is then used as the ASCII value
for one character. This way it is possible to enter any ASCII value, not
present on the keyboard. The console driver also includes a history
function. It is activated by pressing the scroll-lock key. This holds
the display, and enables the cursor arrows for scrolling up and down
through the last scrolled out lines.
The keyboard is configurable to suit the individual user and the differ-
ent national layout.
The keys on the keyboard can have any of the following functions:
Normal key Enter the ASCII value associated with the key.
Function key Enter a string of ASCII values.
Switch Key Switch virtual console.
Modifier Key Change the meaning of another key.
The keyboard is seen as a number of keys numbered from 1 to n. This num-
ber is often referred to as the "scancode" for a given key. The number
of the key is transmitted as an 8 bit char with bit 7 as 0 when a key is
pressed, and the number with bit 7 as 1 when released. This makes it
possible to make the mapping of the keys fully configurable.
The meaning of every key is programmable via the PIO_KEYMAP ioctl call,
that takes a structure keymap_t as argument. The layout of this struc-
ture is as follows:
struct keymap {
u_short n_keys;
struct key_t {
u_char map[NUM_STATES];
u_char spcl;
u_char flgs;
} key[NUM_KEYS];
};
The field n_keys tells the system how many keydefinitions (scancodes)
follows. Each scancode is then specified in the key_t substructure.
Each scancode can be translated to any of 8 different values, depending
on the shift, control, and alt state. These eight possibilities are rep-
resented by the map array, as shown below:
alt
scan cntrl alt alt cntrl
code base shift cntrl shift alt shift cntrl shift
map[n] 0 1 2 3 4 5 6 7
---- ------------------------------------------------------
0x1E 'a' 'A' 0x01 0x01 'a' 'A' 0x01 0x01
This is the default mapping for the key labelled 'A' which normally has
scancode 0x1E. The eight states are as shown, giving the 'A' key its nor-
mal behavior. The spcl field is used to give the key "special" treat-
ment, and is interpreted as follows. Each bit corresponds to one of the
states above. If the bit is 0 the key emits the number defined in the
corresponding map[] entry. If the bit is 1 the key is "special". This
means it does not emit anything; instead it changes the "state". That
means it is a shift, control, alt, lock, switch-screen, function-key or
no-op key. The bitmap is backwards ie. 7 for base, 6 for shift etc.
The flgs field defines if the key should react on caps-lock (1), num-lock
(2), both (3) or ignore both (0).
The kbdcontrol(1) utility is used to load such a description into/outof
the kernel at runtime. This makes it possible to change the key assign-
ments at runtime, or more important to get (GIO_KEYMAP ioctl) the exact
key meanings from the kernel (fx. used by the X server).
The function keys can be programmed using the SETFKEY ioctl call.
This ioctl takes a argument of the type fkeyarg_t:
struct fkeyarg {
u_short keynum;
char keydef[MAXFK];
char flen;
};
The field keynum defines which function key that is programmed. The
array keydef should contain the new string to be used (MAXFK long), and
the length should be entered in flen.
The GETFKEY ioctl call works in a similar manner, except it returns the
current setting of keynum.
The function keys are numbered like this:
F1-F12 key 1 - 12
Shift F1-F12 key 13 - 24
Ctrl F1-F12 key 25 - 36
Ctrl+shift F1-F12 key 37 - 48
Home key 49
Up arrow key 50
Page Up key 51
(keypad) - key 52
Left arrow key 53
(keypad) 5 key 54
Right arrow key 55
(keypad) + key 56
End key 57
Down arrow key 58
Page down key 59
Insert key 60
Delete key 61
Right window key 62
Left window key 63
Menu key 64
The kbdcontrol(1) utility also allows changing these values at runtime.
AUTHORS
Soren Schmidt <sos@FreeBSD.org>
FreeBSD 4.10 January 8, 1995 FreeBSD 4.10